Electric resistance heater



WLJ. DZAACK ELECTRIC RESISTANCE HEATER May 12, 1970 2 Sheets-Sheet; 1

Filed Jan. 29, 1968 INVENTOR. WALTER J Dz AACK A TTORNE 6 BY% I May 12,1970 w. ,1. DZAACK ELECTRIC RESISTANCE HEATER 2 Sheets-Sheet 2 FiledJan. 29, 1968 mA m WA m mm M mm m United States Patent 3,512,114ELECTRIC RESISTANCE HEATER Walter J. Dzaack, Glenshaw, Pa., assignor toEdwin L. Wiegand Company, Pittsburgh, Pa. Filed Jan. 29, 1968, Ser. No.701,157 Int. Cl. H01c 1/02, 1/14; Hb 3/10 US. Cl. 338-241 3 ClaimsABSTRACT OF THE DISCLOSURE An electric resistance heater and method ofmaking the same in which an elongated resistor wire is disposed within ametallic sheath and has terminal conductor portions at respective endsthereof for protrusion beyond one sheath end for connection to a sourceof electrical energy. The resistor wire is supported by an elongateddielectric core having end portions closely fitting within the sheathand a separate, relatively small in cross-section intermediate portionmaintaining the core end portions in spaced relation. The core endportions have circumferentially spaced, longitudinally extendingrectilinear slots for receiving the heating wire and the latter isanchored to respective core end portions and is tensioned therebctweento maintain them assembled with the core intermediate portion.

Preamble Electric resistance heating elements of the so-called cartridgetype wherein a resistor conductor is supported on a preformed, rigid,dielectric core and disposed within a metallic sheath filled with highlycompacted, electricinsulating, heat-conductive material have long beenused.

It has been common knowledge that if the dielectric core could beomitted and the entire space within the sheath filled with the granularmaterial, a more etficient heater would result. However, the dispositionof the resistor conductor in cartridge heaters is such that a preformed,rigid core must be used to support the conductor during its assemblywith the sheath and during filling of the latter with the granularmaterial.

While the present invention does not omit the core in cartridge heaters,it does permit a drastic reduction in mass thereof and this not onlyreduces core costs, it also improves heater efliciency since more ofther mass within the sheath consists of granular material and less ofsuch mass consist of the preformed core.

These and other advantages of the present invention will readily becomeapparent from a study of the following description and from the appendeddrawings.

Description of drawings In the drawings accompanying this specificationand forming a part of this application there is shown, for

purpose of illustration, an embodiment which the invention may assume,and in these drawings:

FIG. 1 is a side elevational view of an electric resistance heaterembodying the present invention,

FIG. 2 is an enlarged sectional view generally corresponding to the line2-2 of FIG. 1,

FIG. 3 is an enlarged fragmentary elevational view of an end of theresistor conductor along with its terminal conductor pin,

FIG. 4 is an enlarged elevational view of a resistor conductor assembledwith its core prior to disposition of the assembly within its tubularsheath.

FIGS. 5 and 6 are respective end elevational views of the subassemblyseen in FIG. 4,

FIG. 7 is an exploded perspective view of the core seen in FIG. 4, and

3,512,114 Patented May 12, 1970 Detailed description With reference toFIGS. 1 and 2 wherein a completed electric resistance heater is shown,such heater comprises a tubular metallic sheath 10 in which a resistorconductor 11 is disposed. The resistor conductor has terminal conductorportions 12 which extend in spaced, side-byside relation outwardly ofone sheath end for connection to a source of electrical energy.

The resistor conductor is supported within the sheath 10 by a preformed,rigid dielectric core 13 and such sheath is filled with highly compactedelectric-insulating, heatconductive refractory material such as powderedmagnesium oxide 14. Although not shown, the sheath end adjacent theterminal conductors 12 may be closed by a suitable plug through whichthe terminal conductors pass while the opposite end of the sheath may beclosed by a suitable plug such as a metal wall which could be welded tothe sheath, crimped therein, or even formed integrally therewith.

As viewed in FIG. 3, the fragmentarily shown resistor conductor is ofthe usual type in which a ressitor wire is in the form of a helicalcoil. Welded or otherwise mechanically and electrically secured to theends of the resistor wire coil are respective terminal conductor pins 12previously mentioned. Although only one end of the coiled resistor 11 isshown in FIG. 3, it is to be understood that its oppoiste end ispreferably identical to that illustrated. Each terminal conductor pin 12is preferably provided with an annular enlargement, or shoulder 12.1intermediate its ends for a purpose later to appear.

With reference to FIG. 4, resistor 11 is adapted to be supported by thecore 13 which is herein shown formed of an end portion 15, an oppoositeend portion 16, and an intermediate spacer portion 17. Each of the coreportions 15, 16 and 17 is formed of a rigid, dielectric, heat-resistantmaterial such as, for example, powdered magnesium oxide mixed with asuitable binder and cured to a solid mass. The core end portions 15, 16are preferably of a transverse size to closely fit within the sheath 10while the transverse size of the core intermediate portion is muchsmaller, and indeed, need only be large enough to possess the necessarystrength to withstand normal handling during the assembly operation.

As herein shown, and as best seen in FIG. 7, the core intermediateportion may be square in cross-section and the adjoining faces of thecore end portions 15, 16 may be provided with respective centrallylocated square recesses 1 8 for closely receiving respective end of thecore intermediate portion. For a reason to appear, the end of the coreintermediate portion adjacent the core end portion 16 will betransversely slotted at 19.

As best seen in FIG. 7, core end portion vided with axially extending,peripheral grooves 20, 21, 22 and 23 which are evenly spacedcircumferentially of the core portion. Thus, grooves 20, 22 are inopposed relation with each other as are the grooves 21, 23. At the endof core portion spaced from the core intermediate portion, arcuate ofgrooves 21, 22 and 20, 23 respectively. Each of the grooves through 25are of a width to receive the coiled resistor 11 therein and each is ofsuch depth that the coiled resistor will be disposed well beneath theouter surface of the core end portion when the resistor is fully seatedin respective grooves. Intermediate the grooves 20 through 23,relatively wide but shallow peripheral grooves 26 are provided for apurpose to appear.

15 is progrooves 24, 25 connect the pairs Still referring to FIG. 7, thecore portion 16 is prefera'bly provided with peripheral grooves similarto grooves 20 through 23 of core portion. Accordingly, the peripheralgrooves of core portion 16 are identified with the same referencecharacters as before but with the sutfix a. Also in a manner similar tocore portion 15, core portion 16 is provided with intermediate shallowgrooves identified with the same reference character as before but withthe sutfix a added.

It is important to note that with the core portions 15, 16 assembledwith the core intermediate portion 17, the peripheral grooves of thecore portions 15, 16 are in axial alignment with each other and suchalignment is assured by the fit of the square core intermediate portionin the square recesses of the core end portions.

While the grooves 20 through 23 of core portion are of a width toreceive the coiled resistor 11, the corresponding grooves a through 23aof core portion 16 are of a width to receive the terminal conductor pins12. Accordingly, grooves 20a through 23a may, depending upon thetransverse size of such pins, be of a somewhat different Width.Additionally, and although not shown, the face of core portion 16 remotefrom the core intermediate portion may be provided with shallow recessescentered at the base of the grooves 20 a through 23a for receiving thepreviously mentioned terminal conductor pin shoulders 12.1.

To assemble the resistor conductor 11 with the core 13, the resistorconductor with it attached terminal pins will be doubled back on itselfto form a pair of legs 27, 28 connected by a bight portion 29 (see FIG.8). The bight portion 29 will then be disposed in the core intermediateportion slot 19 with the legs 27, 28 extending along the coreintermediate portion on opposite sides thereof. The core end portion 15may now be assembled with the core intermediate portion and the resistorlegs 27, 28 extended through respective slots 20, 22.

The resistor leg 27 may now be stretched longitudinally to place itunder slight tension and then doubled over to form a leg 30 joined tothe leg 27 by a bight portion 31. Such bight portion will be disposed inthe arcuate slot of the core portion 15 and the leg then extended underslight tension to dispose its conductor pin in the slot 23a of the coreportion 16, the latter having been previously assembled with the coreintermediate portion 17, with the pin shoulder 12.1 abutting theadjoining end of the core portion 16 to retain the pin in the slot.

Similarly, the resistor leg 28 will be stretched longitudinally to placeit under slight tension and then doubled over to form a leg .32 joinedto the leg 28 by a bight portion 33. Bight portion 33 will be disposedin the core portion arcuate slot 24- and the leg 32 extended underslight tension to dispose its conductor pin in the slot 21a of the coreportion 16 with its shoulder 12.1 abutting the end of the latter.

With the parts thus assembled as seen in FIG. 4, such assembly will 'bedisposed in the sheath 10 with the terminal conductor pins 12 projectingfrom one sheath end. The sheath 10 may now be filled with the powderedmagnesium oxide material from its terminal conductor end, such materialreadily gravitating past the core portions 15, 16 via the grooves 26,26a respectively, to fill all voids within the sheath.

With the sheath filled, it may be swagged or otherwise transverselyreduced to size to compact the powdered magnesium oxide to a rock-likehardness, with the core assembly, the resistor conductor and theadjoining terminal conductor pins embedded therein.

It will have been noted that while core portion 16 is provided with thefour peripheral grooves 20a through 23a, only grooves 21a and 23a haverespective terminal pins 12 disposed therein while grooves 20a, 22a areunused. Nevertheless, it is preferable to provide all four of suchgrooves in core portion 10, even though only two will be used, since byproviding all four grooves, it is unnecessary to orient core portion 16in any particular way with the core intermediate portion 17 other thanto seat the end of the core intermediate portion in the core end portionrecess 18.

In view of the foregoing it will be apparent to those skilled in the artthat I have accomplished at least the principal object of my inventionand it will also be apparent to those skilled in the art that theembodiment herein described may be variously changed and modified,without departing from the spirit of the invention, and that theinvention is capable of uses and has advantages not herein specificallydescribed; hence it will be appreciated that the herein disclosedembodiment is illustrative only, and that my invention is not limitedthereto.

I claim:

1. A cartridge heater wherein an electric resistance wire is disposed ina metallic sheath and wherein such wire has terminal conductor portionsat respective ends thereof for protrusion beyond an end of said sheathfor connection to a source of electrical energy, the improvementcomprising:

an elongated dielectric core disposed within and extendinglongitudinally of said sheath and having end portions proportioned toclosely fit therewithin and an intermediate portion maintaining said endportions in spaced-apart relation, said end portions and saidintermediate portion being separate pieces with the latter smaller intransverse size than the former and with facing sides of said core endportions being recessed to closely receive respective ends of saidintermediate portion, said end portions being spanned by said heatingwire and each core end portion having circumferentially spaced,longitudinally extending rectilinear slots for receiving said wire, saidslots being of such depth that the wire portions are spaced radiallyinwardly of the peripheries of respective core end portions an amount toinsure adequate dielectric clearance between such wire portions and theinner wall of said sheath, said heating wire having a first pair of legsextending from one core end portion to the other and disposed ondiametrically sides of said intermediate portion, and a second pair oflegs extending from said core other end portion to said core one endportion and disposed on opposite sides of said core intermediate portionbetween the legs of said first pair of legs, said heating wire legsbeing joined by bight portions for electrical continuity, the bightportion joining a pair of legs being anchored within a slot in saidintermediate core portion adjacent said one core end portion, saidheating wire being tensioned to retain core end portions and the coreintermediate portion assembled, and compacted electric-insulating,heat-conducting refractory material within said sheath for insulatingthe heating wire and terminals from said metallic sheath. 2. A cartridgeheater wherein a helically coiled resistance wire of U formation isdisposed within a circular metallic sheath and wherein said wire hasterminal conductor portions at its ends which extend outwardly of saidsheath for connection to a source of electrical energy, the sheathcontaining compacted refractory material for electrically insulatingsaid wire from said sheath and for conducting heat from said Wire tosaid sheath, the improvement comprising:

an elongated dielectric core within and extending longitudinally of saidsheath and having end portions circular in transverse section andproportioned to closely fit therewithin and an intermediate portionmaintaining said end portions in spaced relation, said end portions andsaid intermediate portion being separate pieces with the latterrectangular in crosssection and smaller in transverse size than theformer, each of said end portions having a rectangular recess in a facethereof to closely and complementarily receive a respective end of saidintermediate portion, an end of said intermediate portion having aninwardly extending groove to receive the bight of said U formedresistance wire prior to such end being inserted into the rectangularrecess in the face of one of said end portions, the peripheral faces ofeach end portion having a plurality of longitudinal slots to passlengths of the legs of said resistance wire, the legs lying along saidintermediate portion and being stretched between said end portions, theresiliency of the coiled wire pressing the opposite ends of saidintermediate portion into the rectangular recesses in said end portions.3. The construction of claim 2 wherein each leg of said resistance Wireis stretched and passed through slots in and looped over the other endportion, then passed through other slots in said other end portion anddoubled back and passed through other slots in and looped over said oneend portion and disposed in respective grooves in that face thereofopposite the rectangularly recessed face, and then returned throughother slots in said one end portion and overlying said intermediateportion, all out of electrical interengagement with adjacent parts ofsaid resistance wire, said terminal conductor portions passing throughother slots in said other end portion and being connected to the latter.

References Cited UNITED STATES PATENTS FOREIGN PATENTS Switzerland.Great Britain.

VOLODYMYR Y. MAYEWSKY, Primary Examiner U.S. Cl. X.R.

